Process fragments are a cornerstone of process modeling in both Service Oriented Architecture and Business Process Management. The state of the art lacks shared, language agnostic definitions of the basic concepts and properties of process fragments. This absence of a common foundation for the research on process fragments hinders the comparison and reuse of the results in the state of the art, and renders impossible the reaching of agreed, intensional definitions of the different typologies of process fragments. The present work aims at filling this gap by providing a framework of language agnostic definitions of properties of the syntactic structure of process fragments based on the mereotopology of discrete space. Alongside familiar mereologic concepts like inclusion, overlap and disjointness, we cover fundamental concepts for process fragments like (dis)connection, selfconnectedness, borders, interiors and exteriors. Besides providing a foundation for further research on process fragments, we discuss the immediate application of the concepts defined in this work in the scope of the change management of process models.